Most Helpful Guy
Short Answer: No.
There isn't a shred of evidence that supports the thesis that the chance of a guy cheating increases when his partner is pregnant.
I disagree with your characterisation of your coworker's remarks as childish. His cold behaviour towards the girlfriend's pregnancy is a psychological condition experienced by thousands of guys worldwide.
The condition, which is likened to post-natal disorder for women, is well-documented in academic and medical journals. Unlike postnatal disorder that occurs after a woman has given birth, men experience psychological disorders at the onset of a partner's pregnancy. Women too experience the same behaviour as men.
Most Helpful Girl
If the couple allow the baby to drive a wedge between them, then I suppose it is more likely the guy will cheat IF he's a person who would do that anyway. A woman is far less likely to be able to, what with looking after the baby all the while.
Most men are good people, they don't value the wetness of their cock over their side and family. Most men are good husbands, good fathers. This man sounds like a prick.